What is located at the center of our galaxy & how far is the earth from this location?4.

1. What is Pulsar? How is a pulsar similar to a lighthouse?2. If light cannot escape from a black hole, why do we detect X-rays “coming from” black holes?3. What is located at the center of our galaxy & how far is the Earth from this location?4. How long does it take the Milky Way to rotate once? If we assume that the Milky Way formed 13.5 billion years ago, roughly how many times has it rotated?5. Where in our Milky Way galaxy are the oldest stars found? What does this tell us about the formation of the galaxy?6. List three types of galaxy. Which type of galaxy do you live in?7. Explain why astronomers have deduced that galaxies contain a large quantity of “Dark Matter”8. Use Hubble’s Law to determine the distance to a galaxy which is moving away at a velocity of 3,500 km/s. (Assume that H = 70 km/s/Mpc)9. How did humans first understand that the universe is expanding? What type of observations led to this conclusion?10. The Hubble Deep Field is a long-exposure image taken in 1995, which revealed thousands of galaxies, all found in one very small part of the sky. In 2004 a similar, even longer exposure was taken called the Ultra Deep Field. These images have been used to determine that there are about 100 billion galaxies in the observable universe. Assuming that these galaxies are all roughly similar to the Milky Way, estimate the total number of stars in the known universe.